Substudy 06C: A Study of Investigational Agents With Pembrolizumab (MK-3475) and Chemotherapy in Participants With First-Line Locally Advanced Unresectable/Metastatic Gastroesophageal Adenocarcinoma (MK-3475-06C/KEYMAKER-U06)

To join this study, you would need to have stomach, gastroesophageal junction, or oesophageal cancer that has spread or is too advanced for surgery, and you haven't received any prior treatment for it. Importantly, tests must show that your cancer is 'HER2-negative', meaning it doesn't have a specific protein marker. You'd also need to be generally well enough to take part, with healthy organ function, and have at least 6 months of life expectancy.

There are also specific medical conditions that might prevent you from joining. For example, if your cancer is a different type (like squamous cell cancer), or if you have certain unresolved side effects from past treatments. If you have conditions like Hepatitis B, Hepatitis C, or HIV, these would need to be well-managed for you to be considered.

Taking part in this study would involve regular hospital visits for assessments and to receive the medication. You'll have blood tests, scans, and physical exams to monitor your health and how the treatment is working. Doctors will carefully check for any side effects. The study includes several different medicines given in combination, and some of them are investigational, meaning they are still being tested. The exact schedule of visits and treatments would be explained in detail by the study team. You would initially go through a safety phase where the aim is to find the most suitable dose, followed by a phase to see how well the treatment works. You can stop participating in the study at any time.